TEN well-heeled Mercedes-Benz customers in Australia have already formed a queue for what many motoring experts are describing as the ultimate open-air driving experience – the Mercedes SLS AMG Roadster – for not much change from $500,000.

Each will have to wait at least four months for delivery of the made-to-order super-convertible that was formally launched in Australia today, 18 months after the release of the closely aligned gullwing-door SLS AMG Coupe.

At $487,500 (plus on-road costs), the Roadster commands an $18,780 premium over the $468,820 gullwing, although more than half of the extra cost can be attributed to extra standard features such as full leather interior – a $8250 option on the gullwing coupe – and blind-spot warning system ($1650).

Even at $490k, the Roadster is not Mercedes’ most expensive car in Australia, shaded by the $499,200 S-class 65 AMG L.

So far, Mercedes-Benz has delivered 75 of the SLS AMG Coupes since the thoroughbred autobahn blaster arrived in Australia in mid-2010 as a spiritual successor to the legendary Mercedes 300SL that introduced gullwing doors in the 1950s.

The German-built two-seat SLS Roadster – developed in-house by AMG in parallel with the Coupe – loses the gullwing doors and solid roof in favour of two conventional frameless doors and a folding soft-top.

Offered in three colours – black, red and beige – the triple-layer insulated roof can be lowered or raised in a rapid 11 seconds, even on the move at up to 50km/h.

Fitted with a bonded and heated rear window, the soft-top is mounted on a lightweight magnesium, aluminium and steel frame that folds away in a Z shape behind the fixed dual roll-over protection bars.

The roof and its folding mechanism add just 37kg to the overall weight of the topless car – considerably less than comparable all-metal hardtops that are in vogue these days.

The fabric roof not only pays dividends on the weight scales but also in boot space, as it folds on top of the rear bulkhead behind the seats, not in space stolen from the boot.

Compared with the coupe, the Roadster loses just three litres of luggage space – 173 versus 176 litres – due to extra strengthening to compensate for the loss of the coupe’s roof.

Remarkably, the engineers managed to contain the weight gain of the Roadster’s bare ‘body in white’ to just 2kg, for an overall increase of just 40kg – 1660kg versus 1620kg.

In modifying the body, the door openings were deepened into the box-section side sills to make up for the lack of step-in headroom of the high-lifting gullwing door design of the coupe, yet body rigidity is said to be maintained at coupe levels.

The convertible can sprint from zero to 100km/h in the same blistering 3.8 seconds as the gullwing version, making it one of the swiftest production drop-tops in history, shaded on the Australian market by the fastest Porsche 911 Turbo S Cabriolet that does the job in 3.4 seconds.

The convertible Benz uses the same AMG powertrain as the coupe variant, with a thumping 6.2-litre normally aspirated V8 tucked behind the front axle line, joined via a carbon-fibre driveshaft to a seven-speed dual-clutch automatic transmission mounted on the rear axle.

This transaxle layout is frequently favoured in sedan-based race cars, including the upcoming 2013 V8 Supercar ‘Car of the Future’ masterminded by former champion driver Mark Skaife.

In the SLS AMG Roadster, it provides a 47/53 front-rear weight distribution, the same as the gullwing model.

The SLS Roadster marks the last hurrah for the vaunted hand-built 6.2-litre V8, with Benz progressively switching other models to its downsized, more efficient turbocharged 5.5-litre unit.

The free-revving 6.2-litre engine is armed with dry-sump lubrication – another favourite technology of race car engineers – to cut engine height to permit lower installation in the engine bay for a ground-hugging centre of gravity.

Pumping out 420kW of power at 6800rpm and 650Nm of torque at 4750rpm, the big V8 makes the SLS one of the most powerful sportscars in captivity, with more power than the force-fed Porsche 911 Turbo S Cabrio (390kW), but less torque (700Nm).

Top speed is said to be 317km/h.

The seven-speed transmission is claimed to change gears in as little as 100 milliseconds, and offers four driving modes – ‘C’ for “controlled efficiency”, ‘S’ for sport, ‘S+’ for sport-plus and ‘M’ for manual.

All modes are selected by a rotary knob on the console, and the manual changes are made through ubiquitous steering wheel paddles.

The driver can also select a race-start launch function that works electronically with a mechanical diff lock for maximum traction on starts.

The SLS Roadster – like its coupe counterpart – drinks a thirsty 13.2 litres per 100km on the combined cycle, pumping out 311 grams of carbon-dioxide per kilometre.

But the SLS is not the thirstiest passenger car bearing the three-pointed star. That dubious honour goes to the V12 SL600 with a rating of 15.5L/100km.

AMG engineers gave a nod to the environment by introducing fuel-saving measures such as regenerative battery charging – with the generator freewheeling during acceleration and kicking in during braking – and special anti-friction cylinder coatings.

While the gases emitted from the exhaust came in for attention, achieving Euro 5 standard, that other exhaust emission – the engine note – was not overlooked, with Mercedes seeking a symphony of sound, uninhibited by turbos, out of big squared-off twin tailpipes.

The SLS Roadster – available only in full-house AMG treatment – sits on the same aluminium spaceframe as the Coupe, with some steel strengthening in key safety areas such as the A pillars.

To make up for the lack of a roof, the Roadster gets thicker side skirts, additional struts to support the dashboard cross-member against the windscreen frame and centre tunnel, a curved strut between the soft-top and the petrol tank that reinforces the rear axle, and a reinforcing crossmember behind the seats to support the rollover protection system.

The company claims that these measures prevent unwanted vibrations, making it unnecessary to use the additional, weight-increasing vibration dampers often found in open-top sportscars.

The overall result, claims Benz, is a Roadster that is not only refined but performs as well as the gullwing Coupe.

Four-wheel double-wishbone suspension continues the race-engineering theme, with most components such as the wishbones and steering knuckles cast from aluminium for low unsprung weight.

The low-riding chassis squats on a wide track – 1682mm at the front and 1653mm at the rear – further enhancing cornering.

Standard AMG seven-spoke alloy wheels – 19-inch diameter on the front and 20-inch on the back – are shod with 265/35 tyres on the front and 295/30 rubber at the rear.

Again, the wheels are designed with weight savings in mind, as are the race-style composite disc brakes that can stand the SLS on its nose.

Ceramic brakes are optional for a tick under $30,000 for track exponents, along with forged alloy wheels in bare alloy or black paint, should owners want to step up the pace. An even sportier suspension package is optional for track days, priced at $3775.

A rear-mounted spoiler can be raised or retracted with the push of a button, or automatically above 120km/h. On the Roadster, this wing also provides the mounting for the high-mounted stop light in a discreet slit.

Tried and tested rack-and-pinion steering is mounted on the front sub-frame ahead of the engine, again contributing to a low centre of gravity.

Thrillseekers can ease off the electronic stability control to ‘sport’ mode for some tail action, or all the way off if they have nerves of steel. However, one nervous tap of the brake pedal restores the full ESC control.

The cockpit-like cabin has a wing-shaped dashboard – one of several styling cues taken from the world of aviation, including air vents that are supposed to resemble jet engines.

For Australia, the centre console is cloaked in a carbon-fibre finish, although the aluminium-look finish that is standard on the car in Europe is also available as a no-cost option, along with a piano black alternative.

The deep sports seats are sheathed in soft leather, in a range of five colours – or two-tone with black, if the customer prefers.

The door trims, lower dash, transmission shifter and steering wheel are also in double-stitched cowhide.

Because Roadster drivers are likely to want to drop the top in any season, Mercedes’ Airscarf system blows warm air from vents in the top of the seats onto the necks of the driver and passenger

More conventional in-seat heating, keyless entry and start, alarm, Bang & Olufsen sound system and dual-zone climate control are all standard, along with a slot-in glass draught blocker mounted between the headrests. When not in use, the latter can be stored in a special bag in the boot.

Newly available in Australia in both the Roadster and the Coupe is an AMG Performance Media system for track days, showing lap times, 0-100km/h acceleration times, engine data and other functions for full-on drivers.

This package also includes high-speed internet connection with a hotspot in the boot.

Blind-spot warning – a fixture of other upmarket Mercedes models – is standard on the Roadster (but optional on Coupe), apparently to help compensate for the lack of rear-three-quarter vision when changing lanes.

A raft of optional extras are available on the Roadster, including a number unavailable on the Coupe, such as AMG ride control adjustable suspension damping that offers three suspension settings – comfort, sport and sport plus.

Metallic paint – that usual gouge by car companies – starts at a whopping $6475 for the standard AMG version and rises to a breathtaking $29,876 for the “AMG alu-beam liquid metal paint finish”.

The car comes with a tailored car cover and battery trickle-charger, as Benz figures many of these Roadsters will only be brought out on special occasions, otherwise spending a lot of time sitting in garages.

But don’t expect a spare wheel of any sort or even a tyre repair goo can – Mercedes supplies a ‘1800’ roadside-assist number so the driver can phone so the car can be collected on a flat-bed truck and taken to a tyre repair workshop.

The company says the aluminium spaceframe can be damaged by conventional car jacks wielded by amateur tyre changers, hence the special service.

All Mercedes dealerships can sell and service the SLS, which has the usual Mercedes 20,000km service intervals.

While 10 local customers are reported to have slammed down deposits on orders for the Roadster, at least twice as many are expected to join the queue this year.